The research in this proposal examines the role of the endocrine system in the regulation of material behavior. Recently, a role for prolactin in the induction of maternal behavior in the rat has been established. In a series of studies we propose to delineate prolactin's role in the onset of maternal behavior as well as to examine possible endocrine modulation of ongoing maternal responsiveness and the role of hormones in the development of the retention of maternal care. The hypothesis tested is that - The Onset, Maintenance and Events That Promote the Retention of Maternal Behaviors Are Regulated by the Central Actions of Prolactin and Prolactin-Like Molecules. In the initial experiments we define the roles and relationships between prolactin and the steroid hormones, estradiol and progesterone, in the induction of maternal behavior. Then, the relative behavioral potencies of prolactin and prolactin-like molecules are compared. Next, we evaluate the possibility that prolactin may stimulate maternal behavior through its stimulation of hepatic growth factors (IGF- I). Prolactin concentrations in CSF are measured in pregnant and lactating rats using a ventricular push-pull perfusion system in order to see whether prolactin exposure within the brain is measured using in vivo autoradiography to localize potential sites of prolactin action. Then, possible sites of prolactin action are examined by directly applying hormones to discrete neural loci. Experiments also examine the possible modulation of the intensity of maternal behavior by hormones during lactation. Maternal responsiveness in the home cage and in a T-maze is measured in nulliparous rats treated with ectopic pituitary grafts and in lactating rats whose hormone levels have been suppressed. The possible central regulation of ongoing maternal care is also evaluated using a push-pull perfusion system and administration of prolactin to the CNS. Finally, we evaluate whether the rapid retention of maternal care that is set into place during the immediate postpartum period is hormonally-mediated, resulting in permanent changes in neurochemical sensitivities. The results of these studies will increase our understanding of the biochemical and neural regulation of maternal care and provide a basis for evaluating the effects of endocrine imbalances on mother-young interactions.